1. Field of the Invention
Embodiments of the present invention relate to optic waveguide attachment techniques and, more particularly, to low-loss large diameter pigtails.
2. Description of the Related Art
In many fiber-optic applications, it is desirable to attach an optical fiber “pigtail” to larger diameter optical waveguide devices, such as sensor elements. Prior art attachment techniques employ the encapsulation of the fiber in a capillary (tube or carrier or ferrule) with thermally-cured or light-cured epoxy filling the gap between the fiber outer diameter and capillary inner diameter. However, the use of epoxy in the pigtail limits the heat, humidity, and corrosiveness of the environments into which the device is placed.
Further, the use of epoxy typically prevents the pigtail from being fused to the larger device as the heat of the fusion process would melt or burn the epoxy and contaminate the glass. As a result, the encapsulated fiber pigtail is typically epoxied to the larger diameter device. The optical losses associated with these types of pigtails attachments (e.g., due to epoxy in the optical path) are typically at best 0.2 dB. In addition, epoxies have temperature operating limitations that are an order of magnitude below those of glass. Thus, removing the epoxy from the pigtail would allow the device to be used in a wider range of environments, and it could permit the pigtail to be fused (spliced) onto the larger diameter device.
U.S. Pat. No. 5,745,626, entitled “Method For And Encapsulation Of An Optical Fiber” which is incorporated herein by reference, describes a technique in which a 125 um diameter fiber is inserted into a ferrule with an ID of 126 um and heated until the ferrule collapses onto the fiber. However, the restriction of the ferrule ID to 1 um greater than the fiber OD does not allow for relaxed tolerances of the ferrules and fiber. Insertion of the fiber into the close-fitting ferrule is therefore difficult and often results in fiber breakage. It is possible that the need for the tightly matched diameters of fiber to ferrule is due to the fact that the collapse is achieved by heating the glass on one side instead of heating the circumference of the ferrule uniformly.
A method that addresses the circumferential heating of the capillary during a collapse is described in the commonly assigned U.S. Pat. No. 6,519,388, entitled, “Tube-Encased Fiber Grating,” which is incorporated herein by reference. This method uses a laser beam focused on one side of the capillary/fiber combination. The collapse pieces are held in a vacuum chuck in order to aid the draw down of the capillary onto the fiber. The vacuum chuck rotates the collapse pieces about their longitudinal axis such that the laser beam heats its entire circumference. In addition to being rotated, the part is translated along its longitudinal axis within the beam path to achieve the desired collapse length.
While this method heats the part around its circumference, in some cases, the heating may still not be sufficiently uniform and may result in a collapse that “spirals” down the capillary as the pieces are rotated and translated relative to the laser beam. Also, as the system rotates, any misalignment or bend in the capillary or extending fiber may become exaggerated by the centrifugal force, which may causes the piece to bend where the heat has softened the glass creating a corresponding throughput loss. Any air current or other disturbance to the fiber may result in the same bending tendency. Furthermore, since the laser heats the capillary on only one side at any given time, the transition from the non-collapsed to the collapsed region may not be uniform. This may cause the fiber to tend toward the side where the glass first melts, resulting in microbends in the fiber and consequent throughput loss.
Accordingly, there is a need for methods and systems for producing a fiber/carrier pigtail that exhibits low levels of optical loss.